Generating a non-reproducible printed image

ABSTRACT

A method of generating a non-reproducable printed image, for example on a cheque, involves printing a first, background layer of ink on the document, and then printing data on top of the background layer. The ink used to print the background layer is reflective of light of a predetermined wavelength, typically in the infra red spectrum. The ink used to print the data is visually indistinguishable from the first ink, but absorbs light in the infra red spectrum, so that when the printed image is illuminated with infra red light, the image can be discerned. The image typically comprises an encrypted symbolic image and is used for security purposes.

BACKGROUND OF THE INVENTION

[0001] This invention relates to a method of generating a non-reproducible printed image which can be utilised in the production of documents which are not to be copied.

[0002] Valuable documents such as cheques, vouchers, identification documents and the like are subject to fraudulent copying, and various schemes have been adopted in order to make such copying difficult. However, as the technology available to counterfeiters becomes more sophisticated, it is necessary to adopt more and more sophisticated measures to prevent unauthorised copying of such documents.

[0003] an illuminator arranged to illuminate the non-reproducible printed image with light at said wavelengths or range of wavelengths, so that infra red light reflected by the first, background layer of the printed image is passed by the filter, permitting reproduction of the image by the camera.

[0004] Preferably, the filter comprises an infra red filter and the illuminator comprises an infra red light source.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005]FIG. 1 shows data corresponding to an image generated according to the invention, in a text string format;

[0006]FIG. 2 shows the image as printed; and

[0007]FIG. 3 shows apparatus of reading the image.

DESCRIPTION OF AN EMBODIMENT

[0008] The present invention will be described with reference to a practical application in the safeguarding of paper documents which have monetary value, such as cheques or vouchers. It will be appreciated that the described embodiment is purely exemplary, and that the invention has application in other areas as well. In particular, the invention is not limited to use with paper documents, but can be used in conjunction with other substrates such as, for example, credit cards or identification cards, drivers licences, certificates, share certificates, banknotes, labels, identification plates or tags. background ink has no carbon content, while the foreground ink has a high carbon content.

[0009] Most black inks use a high proportion of carbon in order to render them dark. However, it is possible to make use of a mix of pure dark colours which have no carbon in them in order to obtain a “clear black”. For example, a colour mix comprising equal proportions of dark non-carbon based pure colours such as red, green and blue or cyan, magenta and yellow can give a dark shade of grey which is suitable for the above purpose. Certain existing computer printers and plastic card printers are available that make use of inks which are non-carbon based and which are highly reflective in the infra red part of the spectrum. Certain colour ink jet printers, such as the Epson stylus (trade mark) printers make use of non-carbon based inks.

[0010] Before a cheque or voucher is printed, it is necessary to capture the relevant data which is to be represented thereon. This includes details of the drawer of the cheque/voucher, the payee, the date and the amount. This data is sent to a compression software program as an input file, and is read and compressed so that more data can be represented by two dimensional symbols or barcodes which occupy a relatively small physical area. The compressed data is then processed by a forward error correction program which adds parity information to ensure that lost data can be recovered if the two dimensional barcode or image is damaged. This software utilises the Reed-Solomon methodology of creating forward error correction in data streams.

[0011] The data is now processed into symbols which form the readable representation of the data. Unlike known two dimensional barcodes which are created as a bit map image, the symbology utilised is a set of ASCII strings. The letters in the string are interpreted by a specially created font file and thus are converted to symbols when printed. This method was adopted as bitmap images occupy large amounts of memory and tend to significantly slow down

[0012] Since the background ink used to print the image 12 is highly reflective in the relevant frequency range, particularly in the range 850 nm to 900 nm, light from unprinted portions of the symbol is reflected and sensed by the CCD camera. The foreground ink printed over the background ink and representing the printed symbols has a high carbon content with inhibited infra red reflectivity (or enhanced absorption) between approximately 750 nm and 1000 nm. Thus, the CCD of the camera is able to discriminate between the printed and unprinted portions of the symbol and to generate an image thereof. This image is fed to a “frame grabber” or other image capture device, and can then be fed to a PC24 or another device for storage and display. The image is now available as a computer image file for decoding by suitable decoding software.

[0013] By utilising a suitable level of the encryption in the encoded data represented by the image, such as a multi-layer private/public key encryption method, the data itself is adequately safeguarded against attempts to decode or alter it. The present invention enhances the security of such systems by preventing copying thereof.

[0014] Due to the large amount of light reflected by the background portion of the symbol, the CCD camera “sees” this portion of the image as white, whereas those parts which have conventional ink printed on them appear black, and the two dimensional barcode image or symbol therefor is separated or extracted from the background. However, since both inks appear black when illuminated by visible light, conventional imaging devices such as scanners or photocopiers cannot extract the symbols from the background. 

1. Method for communicating data via an optimum data path in a network having a plurality of nodes (u, v, a, b, c, d) connected via data links, the method comprising: determination of an optimum data path from a sending node (u) to a receiving node (v) by determination of all loop-free data paths from the sending node (u) to the receiving node (v) via respective data links and nodes (u, v, a, b, c, d), selection of data paths such that all data to be communicated between two nodes are communicated via the same data path, determination of maximum link utilizations and average link utilizations, or values indicative of combinations of the maximum link utilizations and the average link utilizations of the selected data paths, and defining one of the selected data paths having the minimal maximum link utilization and the minimal average link utilization, or the minimal value indicative of combinations of the maximum link utilizations and the average link utilizations as the optimum data path, and communicating data from the sending node (u) to the receiving node (v) via the optimum data path.
 2. Method according to claim 1, wherein the selection of data paths comprises: determination of data communication capacities of the data paths and selecting data paths having data communication capacities sufficient to communicate the data from the sending node (u) to the receiving node (v).
 3. Method according to claim 1 or 2, wherein the selection of data paths comprises: determination of physical delays of the data paths and selecting data paths having physical delays equal or smaller than a predetermined maximum physical delay.
 4. Method according to one of the claims 1-3, wherein the determination of the optimum data path comprises: definition of an equation system for a linear optimization problem for identifying the optimum data path, and solution the equation system to define the optimum data path.
 5. Method according to claim 4, wherein the definition of the equation system comprises: definition of an objective function for determination of maximum link utilizations and average link utilizations, or values indicative of combinations of the maximum link utilizations and the average link utilizations.
 6. Method according to claim 4 or 5, wherein the definition of the equation system comprises: definition of transport constraints for determination of the loop-free data paths.
 7. Method according to one of the claims 4-6, wherein the definition of the equation system comprises: definition of routing constraints ensuring that all data to be communicated between two nodes are communicated via the same data path.
 8. Method according to one of the claims 4-7, wherein the definition of the equation system comprises: definition of capacity constraints for determination of the data paths having sufficient data communication capacities.
 9. Method according to one of the claims 4-8, wherein the definition of the equation system comprises: definition of physical delay constraints for determination of the data paths having physical delays for respective data links being equal or smaller than a predetermined maximum physical delay.
 10. Method according to one of the claims 5-9, wherein the solving of the equation system comprises: minimization of the objective function regarding the constraints for determining all possible data paths and defining the data path having the minimal maximum link utilization and the minimal average link utilization, or the minimal value indicative of combinations of the maximum link utilizations and the average link utilizations as the optimum data path.
 11. Method according to one of the claims 1-10, wherein the combinations of the average link utilization and the maximum link utilization are represented by a function including the average link utilization and the maximum link utilization weighted with respect to each other.
 12. Method according to one of the claims 4-11, wherein the last solution of the equation system being determined within a predefined time interval identifies the optimum data path, if the current equation system cannot be solved, or if no minimum is determined for the objective function, or the objective function does not converge.
 13. Method according to one of the claims 4-12, wherein the number of variables of the equation system is reduced and/or data links are determined to be considered for the solution of the equation system by determining the time for data communication for all loop-free data paths from the sending node to the receiving node, and identifying the data paths as not to be considered for the solution of the equation system for which a minimum data communication time and/or a data communication time being smaller than a predefined maximum data communication time are determined.
 14. Method of claim 13, wherein data links being included by all possible data paths are considered for the solution of the equation system, and/or data links not being included by any of the possible data paths are not considered for the solution of the equation system.
 15. Method according to one of the claims 4-14, wherein the physical delay constraints are defined by predefined data communication times for the data links between the nodes of the network, and/or the physical delay constraints are defined by transforming band widths of data into respective physical delays.
 16. Method according to one of the claims 1-15, wherein the determination of the optimum data path is performed continuously, or at predefined times, or in predefined time intervals while the amount of data to be communicated is determined continuously, or at predefined times, or in predefined time intervals.
 17. Method according to one of the claims 1-16, wherein maximal amount of data to be communicated.
 18. Method according to one of the claims 1-17, wherein the optimum data path is proved to be the shortest data path by determining the costs for data communication via the data paths, whereby the optimum data path is identified as shortest data path if the optimum data path has the minimum costs.
 19. Method according to claim 18, wherein the data communication costs are determined only for data links including different nodes of the network, and/or the identification of the optimum data path is performed separately for at least two parts of the network, and/or at least one part of the network is grouped to a virtual node and the optimum data path in the remaining portion of the network including the virtual node and the optimum data path in the grouped part of the network are identified separately.
 20. System for communication of data in a network via an optimum data path, the system comprising: a network having nodes connected by data links, at least one of the nodes being a sending node (u) and at least one of the nodes being a receiving node (v), and control means being connected to the network for controlling data communication in the network, characterized in that the control means are adapted to carry out a method according to one of the preceding claims. 